Lead isotopes behavior in the fumarolic environment of the Piton de la Fournaise volcano (Reunion Island)

International audienceThe recent activity of the Piton de la Fournaise volcano offers a rare opportunity to address the issue of Pb isotope behavior in volcanic fumaroles, as the composition of the degassing source is accurately and precisely known. Gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca. 100 degrees C include Na-K sulfate (aphthitalite), Ca-Cu sulfate (e.g., gypsum), Na sulfate (thenardite), Ca-Mg-Al-Fe fluoride (e.g., ralstonite) and native sulfur. The high-temperature deposits show trace element patterns typical of volcanic gas (with Pb concentration up to 836 ppm) while the low-temperature deposits are depleted in most volatile elements (Pb <1 ppm) with the exception of Pd and Tl (in fluorides) and Se (in native sulfur). Only for low-temperature fluoride samples do Pb isotope compositions plot significantly outside the field of lavas. The isotopic shift is ascribed to leaching ubiquitous unradiogenic phases (e.g., sulfides) by acidic gas condensates. The similarity in Pb isotope signature between lavas and sublimate samples more representative of the gas phase (sulfates) indicates that the net fractionation of Pb isotopes resulting from volatilization and condensation processes is smaller than the precision of Pb isotope measurements (better than 60 ppm/a.m.u.). The absence of net fractionation could result from negligible isotope fractionation during Pb volatilization followed by extensive condensation of gaseous Pb, with possibly significant isotopic fractionation at this stage. Although this scenario has to be refined by more direct measurement of the gas phase, and its general applicability tested, it suggests that a small fraction (<10\%) of initially volatilized Pb ultimately escapes to the atmosphere, while the remaining dominant fraction is trapped in sublimates. As sublimates are rapidly dissolved and entrained by runoff, the fumarolic environment appears as a factory efficiently transferring isotopically unfractionated Pb from magmas towards the hydrological system and seawater. Resolving very small isotopic differences between magmas and their gaseous products remains an analytical challenge. High-precision Pb isotope measurements rest not only on instrumental performance but also on high-yield chemistry, as Pb isotopes drastically fractionate (800 ppm/a.m.u.) upon elution on anionic resin. For 50\% Pb recovery, the estimated isotopic bias is plus or minus 60-80 ppm/a.m.u., depending on which of the early (isotopically light) or late (isotopically heavy) Pb fraction is lost. (c) 2012 Elsevier Ltd. All rights reserved

Nuclear field shift effect in the isotope exchange reaction of cadmium using a crown ether

Cadmium isotopes were fractionated by the liquid–liquid extraction technique with a crown ether, dicyclohexano-18-crown-6. The isotopic ratios of mCd/111Cd (m: 110, 112, 113, 114, and 116) were measured precisely by the multi-collector inductively coupled plasma spectrometry (MC-ICP-MS). When the isotope enrichment factors were calculated, the odd atomic mass isotopes (111Cd and 113Cd) showed excesses of enrichment comparing to the even atomic mass isotopes (110Cd, 112Cd, 114Cd and 116Cd). This odd–even staggering property originates from the nuclear field shift effect. The contribution of the nuclear field shift effect to the observed isotope enrichment factor was estimated to be 5 to 30%

The Piton de la Fournaise Volcano (Reunion Island, Indian Ocean): temporal evolution from high resolution Pb isotopes.

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Mass-independent isotopic fractionation of tin in chemical exchange reaction using a crown ether

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Precise analysis of calcium stable isotope variations in biological apatites using laser ablation MC-ICPMS

Laser ablation (LA) is potentially an interesting technique to measure natural variations (delta Ca-44/42) of calcium isotopes in calcium-rich minerals because it allows spatial resolution and avoids micro-sampling and consecutive wet chemistry. We developed a matrix-match sample/standard normalization method and used an Excite 193 nm Photon Machines LA system coupled to a Neptune plus MC-ICPMS to measure delta Ca-44/42 variations in enamel apatite. First, high precision delta Ca-44/42 solution mode (SOL) analyses were performed on a series of 5 crystalline igneous apatite and 6 modern tooth enamel samples, which were micro-sampled using a MicroMill device. The delta Ca-44/42 isotopic values ranged evenly between -0.60 and +0.60(sic) (per amu). Second, we sintered by means of a spark plasma sintering technique the bone ash SRM1400 standard and two synthetic apatites (doped or not with Sr). The Ca isotope compositions using LA were measured in the samples in the raster mode along 600 x 85 mu m profiles and bracketed with the SRM1400 standard. We obtained very good agreement between SOL and LA measurements, i.e. delta Ca-44/42(LA) vs. delta Ca-44/42(SOL) slope of 0.960 x 0.091 (2SE, R-2 = 0.971) and null offset at origin (0.012 +/- 0.084, 2SE). For all samples, residual values to the 1 : 1 slope were \textless= 0.1& (per amu). However, an unexplained and constant 0.13& offset occurred when considering the Ca-43/42 ratio, suggesting an uncorrected isobaric interference on Ca-43 in the LA mode. We also noticed that the doubly charged strontium (Sr) interference correction is of crucial importance for accurate matching between LA and SOL measurements. In the SOL mode, Sr is discarded by ion chromatography leading to typical Sr-87(2+)/Ca-44(+) ratios of 10(-5) to 10(-6). In the LA mode, this ratio can exceed 10(-3). We show that the value set for the Sr-87/Sr-86 ratio is of importance to correct the Sr interference, and that optimized residuals to the 1 : 1 slope are obtained using a Sr correction that takes into account a mass fractionation factor for doubly charged Sr distinct from that of Ca. We found that deciduous teeth enamel is depleted of Ca heavy isotopes by about 0.35-0.40(sic) (per amu) compared to wisdom teeth enamel, a shift compatible with a transition from a milk based diet to a plant and meat based diet

The Piton de la Fournaise Volcano (Reunion Island, Indian Ocean): temporal evolution from high resolution Pb isotopes.

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Preliminary Results from a New 157 nm Laser Ablation ICP-MS Instrument: New Opportunities in the Analysis of Solid Samples

International audiencePreliminary results are given from an excimer 157nm laser ablation multiple-collector inductivelycoupled plasma-mass spectrometer (LA-MC-ICP-MS),used for the isotopic measurements of solidmaterials. Elements of geological interest withdifferent volatilities such as pb and U (e.g. zircongeochronology) and Cu and Zn (as examples ofgeochemical/biochemical tracers) were analysed.The range of ablation rates of 20-150 nm 5-1enabled us to ablate the sample down to a depthof 45 f!m for a 50 f!m diameter pit. The Cu and Znisotopic measurements gave values that were verystable with, on average, a 0.01% standard error,comparable with that achieved in liquidmode measurements

The lunar neutron energy spectrum inferred from the isotope compositions of rare-earth elements and hafnium in Apollo samples

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Experimental and Theoretical Investigation of Isotope Fractionation of Zinc between Aqua, Chloro, and Macrocyclic Complexes

International audienceThis work reports on the chemical isotope fractionation of Zn(II) by a solvent extraction method with the crown ether dicyclohexano-18-crown-6. The (m)Zn/(64)Zn ratios (m = 66, 67, and 68) were analyzed by multiple-collector inductively coupled plasma mass spectrometry. The relative deviations of the (66)Zn/(64)Zn ratios relative to the unprocessed material (delta(66)Zn) was determined to be -0.51 to -0.32 in the acidity region 1.0-6.0 mol dm(-3) (M) HCl. The acidity dependence or delta(m)Zn was explained by the isotope exchange reactions between Zn(II) species (Zn(2+), ZnCl(+), ZnCl(2), ZnCl(3)(-), and ZnCl(4)(2-)) and the mole fractions of them. The magnitude of delta(m)Zn due to the related Zn(II) species estimated by quantum chemical calculations was in agreement with delta(m)Zn experimentally obtained. Contribution of nuclear field shift to the isotope fractionation was estimated to be less than 10% of delta(m)Zn by quantum chemical calculations